To study the modifications of membrane components, mainly proteins, that occur in cells transformed by a temperature-sensitive mutant of Rous Sarcoma virus; the study of the role of these modifications in properties of the cell that are expressed at, or mediated by, the cell surface. Isolation of cell membranes by differential and density gradient centrifugation. Analysis of the membrane composition by electrophoretic and chromatographic techniques. Study of the surface topography by use of enzymic labeling with I125 or tritium, combined with electrophoresis.